The present invention relates generally to machine control, and more particularly to automatic control of a joystick for dozer blade control.
Automatic control systems for dozers have become increasingly popular in the construction equipment market. In an automatic control system, the position and orientation of the working implement (blade) of the dozer is determined with respect to a design surface; the blade is then automatically moved in accordance with the design surface. Automatic control systems are used, for example, to accurately produce design surfaces for the construction of building foundations, roads, railways, canals, and airports.
Automatic control systems have several advantages over manual control systems. First, manual control systems generally require more highly-skilled operators than automatic control systems: proper training of operators for manual control systems is both expensive and time-consuming. Second, automatic control systems increase the productivity of the machine by increasing the operational speed, permitting work in poor visibility conditions, avoiding downtime due to manual surveying of the site, and reducing the number of passes needed to produce the design surface. Third, automatic control systems reduce consumption of fuel as well as consumption of construction materials (construction standards call for a minimum thickness of paving material such as concrete, asphalt, sand, and gravel to be laid down; if the underlying surface is inaccurately graded, excess paving material needs to be laid down to ensure that the minimum thickness is met).
The operating principle of an automatic control system is based on the estimation of the current position and orientation of the dozer blade edge with respect to a reference surface defined by a specific project design. The reference surface can be specified in several ways. For example, the reference surface can be represented by a mathematical model, referred to as a digital terrain model (DTM), comprising an array of points connected by triangles. The reference surface can also be specified by natural or artificial surfaces and lines. A physical road surface is an example of a natural surface that can be used as a reference surface: the physical road surface can be used as the target for the next layer. Artificial surfaces and lines can be created, for example, by a laser plane or by metal wires installed on stakes.
The position and orientation of the blade can be determined from measurements by various sensors mounted on the dozer body and blade. Examples of sensors include global navigation satellite system (GNSS) sensors to measure positions; an optical prism to measure position with the aid of a laser robotic total station; electrolytic tilt sensors to measure angles; potentiometric sensors to measure angles and distances; microelectromechanical systems (MEMS) inertial sensors, such as accelerometers and gyros, to measure acceleration and angular rate, respectively; ultrasonic sensors to measure distances; laser receivers to receive signals from a laser transmitter and to measure vertical offsets; and stroke sensors to measure the extension of hydraulic cylinders.
Measurements from the various sensors are processed by a control unit to determine the position and orientation of the blade. The measured position and measured orientation of the blade are compared with the target position and target orientation, respectively, calculated from the reference surface. Error signals calculated from the difference between the measured position and the target position and the difference between the measured orientation and the target orientation are used to generate control signals. The control signals are used to control a drive system that moves the blade to minimize the error between the measured position and the target position and to minimize the error between the measured orientation and the target orientation.
The position and orientation of the blade are controlled by hydraulic cylinders. A valve controls the flow rate of hydraulic fluid, which, in turn, controls the velocity of a hydraulic cylinder (the velocity of the hydraulic cylinder refers to the time rate of change of the extension of the hydraulic cylinder). Valves can be manual or electric. For current automatic control systems, electric valves are used, and the control signals are electric signals that control the electric valves.
If a dozer is currently outfitted with manual valves, retrofitting the dozer with electric valves can be a complex, time-consuming, and expensive operation. In addition to modification of the valves, the hose connections to the pump, tank, and cylinder lines need to be disconnected and reconnected; retrofitting operations can take up to two days. As an added complication, in some instances, retrofitting an existing dozer may not be permitted by the manufacturer under terms of sale and may void the warranty for the dozer.
Even if the dozer is already outfitted with electric valves, the interface to the controller for the electric valves can be proprietary. The manufacturer of the dozer can restrict access to the interface specification needed by the construction contractor to install a custom automatic control system. And again, in some instances, retrofitting an existing dozer with an automatic control system not supplied by the manufacturer may not be permitted by the manufacturer under terms of sale and may void the warranty for the dozer.
Construction contractors can of course purchase dozers with electric valves and automatic control systems installed by the dozer manufacturer. In some instances, however, construction contractors lease or rent dozers, and the dozers available for lease or rent may not have suitable automatic control systems. Construction contractors may also wish to retrofit existing manually-controlled dozers with automatic control systems or to upgrade automatic control systems supplied by the dozer manufacturer with custom automatic control systems, which can have different capabilities or lower cost than the automatic control systems supplied by the dozer manufacturer.